package com.alvinlkk.basic.chapter21;

import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

class TaskPortion implements Runnable {
    private static int counter = 0;
    
    private final int id = counter ++ ;
    
    private static Random random = new Random(47);
    
    private final CountDownLatch latch;
    
    public TaskPortion(CountDownLatch latch) {
        this.latch = latch;
    }
    
    @Override
    public void run() {
        try {
            work();
            latch.countDown();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    
    public void work() throws InterruptedException {
        TimeUnit.MILLISECONDS.sleep(random.nextInt(200));
        System.out.println(this + " complete");
    }
    
    @Override
    public String toString() {
        return String.format("%1$-3d ", id);
    }
}

class WaitingTask implements Runnable {
private static int counter = 0;
    
    private final int id = counter ++ ;
    
    private static Random random = new Random(47);
    
    private final CountDownLatch latch;
    
    public WaitingTask(CountDownLatch latch) {
        this.latch = latch;
    }

    @Override
    public void run() {
        try {
            latch.await();
            System.out.println("Latch barrier passed for " + this);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    
    @Override
    public String toString() {
        return String.format("%1$-3d ", id);
    }
}


public class CountDownLatchDemo {
    static final int SIZE = 100;
    
    public static void main(String[] args) {
        ExecutorService exec = Executors.newCachedThreadPool();
        CountDownLatch latch = new CountDownLatch(SIZE);
        for(int i=0; i < 10; i ++) {
            exec.execute(new WaitingTask(latch));
        }
        
        for(int i=0; i < SIZE; i ++) {
            exec.execute(new TaskPortion(latch));
        }
        System.out.println("Lauched all tasks");
        exec.shutdown();
    }
}
